Does Running A/C Really Affect Gas Mileage?

We should all try to conserve fuel, whether for the environment or our pocketbooks—or both.

It is with this notion in mind that we address an age-old question:  Is it more fuel efficient to drive with the A/C running, or with the windows rolled down?

We’ve all heard the arguments:

“Opening the windows increases aerodynamic drag, so more fuel is needed.”

“Running the A/C puts extra load on the engine, so more fuel is needed.”


The truth is, both statements are correct, but which is “more” correct?  The answer depends on several things, including the  type and size of car you drive, the speed you are driving, the temperature outside and the condition of your A/C system.

Studies have shown that using the A/C in your car does lower your car’s fuel efficiency by an average of 3 miles per gallon depending on the age and size of your car. A/C lowers your fuel efficiency because it diverts  energy from the engine to power the car. The fuel to power the A/C has to come from somewhere, and the engine is the most efficient way for the A/C to get its energy.

However, if you’re driving at high speeds, leaving your windows down can actually lower your fuel efficiency MORE  than using your A/C would. Lowering your windows can lower your fuel efficiency because the wind entering your car creates a drag that forces your car to work harder to get to the same speed if the windows were rolled up.

Regardless of whether you choose to use the A/C or roll the windows down, there’s no method to cool your car that doesn’t lower your car’s fuel efficiency. Choose the method that makes you the most comfortable while driving. A car that is too hot can lead to drowsy or distracted driving, which can eventually lead to a crash. Both options lower your vehicle’s fuel efficiency, but not by enough that you shouldn’t use either method to cool your car, especially during the summer.


  • A good rule of thumb is if temperatures outside the car are pleasant, open the windows and let your car cool down for a few minutes before using the vent or A/C on low to keep a comfortable air flow in the car.
  • Your air conditioner works hardest when your car is the hottest. Take steps to reduce your need to run the A/C on full blast for long periods by parking in the shade or venting the hot air through open windows or sunroof before turning on the A/C. This will allow some heat to escape the car before you put strain on your A/C.
  • When travelling at speeds over 40-45 mph, keep your windows up and use your A/C on a moderate setting. When travelling below 40 mph put your windows down to keep cool. Remember, running the vent does not burn extra fuel.
  • An important consideration is the size of your vehicle. Body/engine size impact heavily on A/C.  Large vehicles have bigger engines, but also have more area to cool. A smaller automobile with a smaller engine can be cooled more efficiently. That is something to consider when purchasing your next vehicle, especially if you have a long commute

LMK 2020